Field of the Invention
The present invention relates to substrates for microscopy, and more particularly to repositionable substrates for microscopic applications.
Description of the Related Art
One of the disadvantages of the scanning probe microscopes (which include such devices as atomic force microscopes and scanning tunnelling microscopes) is their very small field of view. Consequently, it is difficult to relocate a work area on a substrate once this work area is moved out of the field of view (i.e. away from the tip).
It is therefore desired to develop a way to reposition a work area on a substrate at the tip of a scanning probe microscope. One approach to this problem has been to integrate another microscope, such as an optical or an electron microscope, into the scanning probe microscope to provide images of the substrate and the tip. See, e.g., Yasutake et al., "Scanning tunnelling microscope combined with optical microscope for large sample measurement", J. Vacuum Sci. Tech. A 8 (1) 350-53 (Jan/Feb 1990) and McCord et al., "Lithography with the scanning tunnelling microscope", J. Vacuum Sci. Tech. B 4 (1) 86-88 (Jan/Feb 1986). This approach adds to the complexity of the apparatus. Moreover, there are other drawbacks to using these large-field microscopes to position the sample. Electron microscopes operate under vacuum, a serious drawback for practitioners who wish to work with biological specimens. Optical microscopes work well for materials which are visible down to the 1-10 .mu.m scale, but not for smaller objects. Moreover, it is difficult to configure an integrated optical-scanning probe microscope to image the point of contact of the tip and the substrate.
Coded substrates have been developed for these applications. For example, Yasutake et al. teaches the use of substrates 10 patterned with number pairs 12 to provide x,y coordinates for the substrate surface, as shown in FIG. 1. However, this type of substrate practically requires the use of an integrated large-field microscope, because it is time-consuming for a scanning probe microscope to image numerals and other symbols.
Other approaches use capacitive or interferometric sensor systems to precisely position a substrate relative to the scanning tip. These approaches provide a calibrated x,y positioner for accurate repositioning of the tip with respect to the substrate. However, it is questionable whether, using these approaches, the substrate can be removed from the scanning probe microscope head and then replaced in the head with great precision.